You want LAND tax records to follow the land. 

Personal Property was things like slaves, horses, and tithable 
males (men old enough to work)  etc. 

I use tax records a LOT to find families.  
Land records will often say something like "last assessed 
to John Smith" which is a clue who he got the land from. 
(depends on how thorough the tax assessor was.) 
Personal tax lists will include sons age 16-21 in the 
household as taxables under their father, or their guardian. 
This depends on the year...some records give more 
information than others.  
I have found it is important to read every year available.
You may find John Smith for several years with 3 tithables, 
and then one year John Smith has 2 tithables, and the name 
Bob Smith appears.  It is a very strong clue that Bob was his 
son who has now set up his own household.  
Also, by reading every year, and looking for everyone with the 
surname of interest, you can sometimes find a widow.  
Say John Smith disappears from the personal tax lists in 1770.
Then Ann Smith shows up in 1771, 1780, and 1787.  
You have clues to his wife, and how long she may have lived. 
(You want to read all Smiths, just to be sure there is not also a James 
Smith who died in 1770, 1779, or 1786, who she might be widow of.) 
Listing of widows on tax records (in my experience)  was somewhat
erratic.  Many times the assessor would skip her.  Sometimes he 
would list her name, and mark her as not tithable.  Or, she could 
be listed with tithable males...sons between 16-21.  
If the people did not own LAND, the personal lists are often your 
only clue of where and when they lived. 

A lot of things can be IMPLIED from tax lists.  For instance, an older 
man is more likely to own more assets.  
Remember, these are all CLUES. 
I always read all adjoining counties, too.  That sounds like  a lot of 
work, but it really pays off.  Tax lists may tell you if he had the same
neighbors/associates as his father did 20 years earlier.   Did a group 
of people come from another area together?  Are they all here together?

One more note :  The land tax records of Monroe Co., (W) Va. from 
1800 onward list name, tract, acres, and neighbors and rivers....
and even the distance from the courthouse !  
It is a tremendous list !  Not all of them are this complete. 

I have not seen very many occasions at all where another 
adult was counted with the head of household. The tithables 
ages 16-21 could include servants (not slaves) as well as sons, 
although by the time period you would find most of these tax 
records, indentured servants were pretty rare.  I usually assume 
they are sons, unless I find other evidence. 
A single adult man, even if living in someone else's house hold, would 
be listed as a single freeman.  He would, after all, be responsible 
for his own tax.  
The head of household would only pay the tax for the minors who 
were working on his farm. 
In Penna., the single freemen are usually on a separate list at the 
end of the regular list.  In Va., the names are usually all mixed 
together.  If a man is taxed on himself, and little or no property, 
you can usually assume he is a single freeman, especially if this 
is the first time his name appears.  
Just to be sure, I always check surrounding counties to see if he 
has moved from a neighboring area, instead of being a man who
has just become taxable in his own right for the first time. 

Tax records can help too, when a man buys a piece of land, lives there
thirty years without every suing anyone, buying more land, etc. He is
there, 
but won't appear on any other records.  But he will be taxed every year.
MANY times I have found people on tax records, who are absent on 
census.  I have some  "hillbillies"  who distrusted authority, wouldn't 
talk to the census taker, or witness deeds.  Some of these people are
"absent" for 30 years on census, but they had to answer to the tax man.
If they did not reveal their assets to him...that is when you find
records 
saying "suit against so-and-so for refusal to pay tax..."  

Another thing I thought of....In Virginia estates, slaves were considered

real property, like land.  (This made for lots of lawsuits when real
property
died.)  In Maryland slaves were personal property in estates.  But in 
both places, you are likely to find slaves as personal property on tax
lists. 
(I have families I have been able to prove because they were suing 
each other over how to divide up the slaves of the deceased.  Land 
can be divided much easier than slaves!) 

As I said, I love tax records.  I appreciate the comments people have 
sent me about my ruminations on the subject.