It is usually just a lot more safe and convenient to ask someone to help. Also the launch/land moment gives you a nice little time to chat.
Quite often I help someone land, ask for the conditions out there, double check my kite size is optimal for the conditions, and then that person would help me launch
Also even the best of scenarios for self launch/land are not that great.
e.g. for a beginner:
I am thinking the best/safest scenario for self launch/land is knee-deep low-ish wind flat water spot where you can "drift launch".
Even here I would prefer a helping hand because your lines can get inverted if you lose attention for a bit or are just unlucky.
The safest way to self land there is just pull the quick release out on the water.
Doing that means getting a wet kite.
When you get more advanced you can also look at different launch/land techniques but again the spot must be suitable for the technique (e.g. enough clear beach without obstacles)
and there will always be more risks involved compared to have someone help you.