safety margin in transistor base current
Any fixed factor like that is mostly superstition.  The point is to make sure the transistor saturates if you want low C-E voltage, which you usually do in a switching application.  Generally you know or can specify the highest collector current the transistor must support and you know the minimum current gain from the datasheet.  Dividing those two yields the minimum base current you must supply.  You have to do some calculation to determine the base current you need, so you might as well do the right one.  Using bad numbers doesn't make it easier, just less useful.  It's not like doing this divide is any significant work or burden.

Once you know the minimum base current, you find the voltage accross the base resistor, and divide the two to get the maximum base resistance.  This is the place to apply some judgement now that you have a meaningful value.  Good engineers know that stuff happens and you don't want things to operate right on the edge of correctness.  Once you have the maximum base resistor you can make it a bit or a lot lower depending on other issues in the design.  Almost always I would go down at least a couple of standard values from the maximum, but there are times when every uA matters and you want to think about it carefully.  A factor of 10 is gross overkill in most situations unless there are other constraints you haven't mentioned.

There is one possible reason you might want to saturate a bipolar transistor by a wide margin.  The C-E voltage flattens out once the transistor saturates, but it still goes down a little with increased base current.  If extra low C-E voltage is more important than higher base current, then it can be worth overdriving the transistor by 10x.  Generally if on state voltage is so important you'd use a FET though.

One case I can imagine, admittedly a bit contrived, is you have enough current to switch so that a little lower C-E voltage matters for dissipation or voltage loss in the system and you are driving the switch from a low voltage circuit that has a good amount of current available.  FETs don't work well with gate voltages as low as a B-E junction drop, so driving a FET in this situation would require extra parts and higher voltage.  A overdriven bipolar transistor could be a good answer in this case.