Guts, Sorry to repeat coz I am really curious: Why I have to keep running Cardano data node (vith DM app)? What are benefits of such energy spending to me personally ?

You don't "have to", you have choices in wallet apps but there are tradeoffs. Daedalus is a "Full Node" wallet app; it downloads the entire Cardano Blockchain directly and verifies it with your computer. This gives you the best accuracy and trust into your wallet balance numbers at any given time. At present, all other Cardano wallet apps are "light wallets"; these are essentially services that download and verify the Cardano Blockchain on your behalf and then let you scan their database for your transactions. Light wallets allow you access without the extra effort, but you have to trust the service provider.

If you mean the node inside Daedalus (I don't know what “DM” is), there are none. Use a light wallet instead. There are also hardly any benefits for the network in letting it run.

Daedalus has to stay synced to function, if you want a wallet that does not require being online all the time and have long sync periods you would want to pick a different wallet like CCvault Typhon wallet Yoroi etc