I do daily smoke. I use cannabis to help me with nausea, appetite loss and sleep deprivation caused by the medications I am currently on. It's also beneficial for me to have lower blood pressure which cannabis has been accredited with in some research. Cancer prevention is another reason that I use cannabis, there has been some claims that cannabis can help prevent or cure cancer. Since I have a higher risk of some forms of cancer due to a terrible medication I was on that ended up not working anyways I like to think cannabis may help as a preventative measure. One last reason is that some research has linked it to being beneficial to help balance the immune system which would be great help for my condition.
For daytime smokers I would recommend this bud for sure. You'll see that a large part of my reviews are on fruity flavored sativas. I find those are my favorite daytime buds. Anything with citrus type names are a good indication that it is a sativa. Lots of the indica's are usually more of the heavy hitters that will knock you out at night. Also if you have a microscope and can look closely at the trichomes, the clear ones will be best for a daytime high. Once the trichomes start to go into the amber colored that means the THC is likely degrading to CBN which will make you drowsy.
As far as negative mental effects I would have to say yes. Cannabis can have a negative effect of memory and ambition. Also heavy smokers usually either don't dream or don't remember their dreams which means missing out on a whole other reality that you can be experiencing. I also agree with Kief Preston that I do sometimes have less patience, but I can't say that's for sure a result of cannabis consumption.