Would you buy an extra lot?

The empty lot behind my townhome may be offered to me for a private sale. It's just grass and brush now. I'm uncertain about whether to buy it. If you've done this (or chosen not to) in Houston, what was your experience? Does the city combine both lots into one when considering property taxes? Are you limited on what you can do with the lot? Would you recommend a real estate lawyer? For reference, this is in the Spring Branch area. If I don't buy it, 2, 3 story townhomes will go up directly behind me, like 6 feet from my place probably.