I started playing a 5 string in the mid 80's not to be fashonable, but so I wouldn't have to tune down to E flat, D or D flat etc. instead of getting a Hipshot De -Tuner, playing covers from Sabbath, Van Halen and all those tuned down tunes

) I figured it was better to have the lower string, since then I have moved on to 6, 7, 8, 12 string and Chapman Stick, but I still have some 4 strings and enjoy playing them.
Some of the material I cover can't be played on a 4 ( like Dream Theater ) the tuning and harmonics, but do I use the extra strings all the time ? No, I play what the song requires and use the other strings to incorporate some of my own ideas into what's already there.
Bass playing has come such a long way and there are so many talented players, 4, 5, 6 etc. people have played/used more than 4 strings since the 1960's , its all about trying something different and breaking the rules and pushing the boundries of the instrument, the sky is the limit.
Bruce