It's about multiplying the potential loads.
So the answer is it depends on the things you hook up to them. For the purposes of argument, we will assume that all the connections are solid.
If you have 4 strips together, A, B, C and D, each one with 4 outlets on it, then you get 3 outlets for use and 1 to continue the chain (with 4 on D since it stops there).
If you plug in 4 things to D then its cord supports the load of those devices. If you plug three things into C then its cord supports those three things *and* the current for D. By the time you get to cord A, at the start of the chain its cord is carrying the load of all of the devices further along.
This is where it gets dangerous, since you can quickly exceed the current rating for the cord (or the outlet iself), and excessive current heats up the wires, melts the plastic and then it can short out and catch fire.
If all the things you connect up are very low power (like cellphone chargers, a laptop charger, VCR, DVD player etc) then you cut the risk of overdoing the current considerably, but they do add up.
Higher power devices like TVs, amps, computers, heaters, AC units, kettles, vacuum cleaners etc are most certainly not suitable for this sort of daisy chaining.