Is it also so they can "legally" show people around properties that they don't own, but just have a piece of paper that says they or someone else intends to buy it one day? 

Legally they are supposed to be neutral but it is impossible to ensure that. 

The idea of hanging on to it for an investment purpose when I already have it and want to head into the investment property business makes sense, but only if I can do it legally, feasibly and financially efficiently. 

I use this format: PETIOProperty - type, description and rough as-is and ARVEquity - value less recorded mortgages and liensTitle - Record owner, entity or living or deceased person(s)Interest(s) - if owner is a deceased individual, need to know who legal heirs areOpportunity - specific ways to benefit, such as buy, fix and sell, or fix and rent, etc.You'll need a working knowledge or someone who can research title for you.

.- Someone who has an EXTENSIVE network of contacts (builders, contractors, legal) to get me in touch with (not a 1-deep list of overpriced buddies, people with solid references and track records).  

As long as you do that (allow them the ability to have them installed, and don't "prohibit" the modification) then you have made a reasonable accommodation and are ok as far as the ADA/fair housing goes.Obviously you really should read the appropriate portion of the act yourself, and if you have any doubts or questions seek appropriate legal counsel.

I'm no legal expert here, and invite corrections from anyone if this is wrong or unclear!

If done properly and legally you have purchased the "right" but not the "obligation" to purchase the property at the stated price.

Often they are two separate business lines since title companies can not legally practice law - which is doc prep.  

Sometimes sellers tell you rents are below market but what they don't tell you is that their tenants are not willing to pay the higher rent and they have "professional bad tenants" - or tenants who know the system and they are staying in the properties rent free and they are using every legal loopholes to do so.