It's not. It's raising the possibility of burning your house
)) ok lets put it that way, when you use one lamp on one socket with some tiny wire, lamp is using 60W and everything seems to work fine. But once you add 3x40W, you are using 120W instead of 60W. 120W usually is not really a big deal, but 240W on one chinese non ceramic spliter can be a bit too much.
e.g.
1. I have 0.75mm cable wiring setup. I went to google and it said that this can support ~1400W of load/6A of current.
http://www.diynot.com/pages/el/el003.php
2. I have chinese Y splitters some plastic crappy ones which should be ok with 150W, but I would be afraid to put more wattage per splitter.
If you would connect vacuum cleaner, it would not work less effectively, device would consume more watts a cable can handle and therefore cable can melt from the heat and lit up the building
So check out what you have and how many watts can those items support and don't overuse it and you will be fine