Some people live in a travel bubble. If my company has a $125/night travel policy it doesn't mean I can't spend $190 if that is the best option for that night. As long as I do my best to make up for it with a 5 night stay at a Candlewood for $89/night it will all even out. So if I find a HIX that is going for $119/night but $134 will get me 5k bonus points, I don't think twice about booking the bonus points. I know that in the end my budget will even itself out because I am smart about it.
Is it possible that I could get my average down to $114 over the course of a year by not booking bonus points? Sure, I guess, but that's not how it works. You get a budget number to try and stick to, otherwise your company may as well tell you to stay at Motel 6 for 100 nights and then treat yourself to a few Hiltons. This thread makes me really happy to work for a company that trusts me to stay 200-250+ nights a year booking my own travel and knows I won't abuse the system.
Reaching top status at multiple hotels has tons of benefits that can't be priced in, as noted above by a poster, such as free internet or food, but even more so just in getting things by asking because you are a top tier, such as a lower rate (which I have used all the time just by calling and asking and receiving) or free parking or just the ability to get a room in a tough market during busy events.
To suggest it is stealing or morally wrong to book some bonus points is a ridiculous claim. Most companies have a chain of command where you have your expenses approved by one and probably two people, who both look at your expenses and then decide if they are ok. $5 or $10 here or there when you will make up for it in other ways is hardly something to worry about, especially when the benefit of having a solid employee on the road for you for tons of nights a year far outweigh a few hundred bucks over the course of the year.