The essence of the measure includes turning off any kind of equipment which currently is not needed for the defined time period. As the rule of a thumb we shall consider that it may be effective if the time in a turned-off mode is at least 4 times more than the time of "switch on" and "switch off".
This means that for short time periods turning off is not effective and is not included (for example 1 minute break for computer working session does not require turning off and on the computer, as its turn off and turn on time is also ca. 1 minute, etc.).
Examples of equipment are typical home-based equipment "service-bases": computer/monitor, notebook, printer, TV, X-Box, electric training equipment, smartphone (connected to socket), music equipment, synteizer, router, etc. Typical installed capacity of such equipment for average appartment is 400-700 W.
Usually it works in average for 4-6 hours/day (at least main part of it).
The optimization of turning off may provide up to 5% economy (i.e. 0.2-0.3 hours or 12-18 minutes). For consistency and conservativeness let's say that 50% of installed capacity may be used in once (550/2=275 W).
Then the daily economy is 275 W*5 hours=1375 Wh * 5% = 68.7 Wh.
Then, for the year it will be 68.7 Wh * 365 =25 000 Wh (25 kWh). Bearing in mind that the average annual consumption for average appartment is 100 kWh/month (1 200 kWh/year), it will comprise at least 2% (and up to 5%) from total consumption/ bills.
No investments, just creating saving habit.