What are the effects of crown lengthening?

Bone loss & 2 others. Main effects are : 1 . increased amount of available tooth to support and retain the crown as well as allowing sufficient reduction for best bite level location and 2. Possible sensitivity due to exposed root -- often need Root Canal treatment to eliminate feeling in the tooth. Ask your Dentist about these. It can be a most worthwhile treatment. Also ask about option of extraction and implant.
Discomfort perhaps.. Crown lengthening is done when what is left of the tooth above the gums is too short to work with. So you are numbed up and some bone and gum tissue is removed. It is not always painful or uncomfortable. It depends on your tolerance and how much is removed. That said, i would expect perhaps a little discomfort following the procedure.
More tooth . Crown lengthening is to aid the dentist in providing enough space for a crown to be placed with out invading the bone and gingival spaces. It is needed to get below the defects created by decay and/or fracture. It can be very beneficial but has limitations as well. Talk to your dentist about it.
Function or esthetic. Functional crown lengthening is an important part of your overall oral health, appearance, comfort and function. You also can improve your “gummy” smile because your teeth may appear short. Whether you choose crown lengthening to improve function or esthetics, the benefits are both great.