A few reasons for getting one.
I currently drive to work because I'm, well, lazy, and enjoy the comfort.
Reason 1 - not going to be able to drive to work soon
Soon I'll have no choice other than to cycle or take the bus, because we're moving offices and there will be no parking there!
A bus journey would be inconvenient because I'd have to take the bus to the central bus station, and then back out to towards the railway station which goes past my work. The buses in Cambridge are often delayed or slow, or sometimes cancelled, and even if bus wasn't stuck in traffic, and I was able to transfer with no delay, it would take me 35 minutes to get to work.
Reason 2 - Consistent Journey Time
A car journey to work takes between 20 and 40 minutes to do the 6.8 to 8.1 miles (depending on what Waze tells me is best). Thus the best I can do is 20.4mph, but can be as little as 12mph! And that's only possible because my employer is happy for me to start and finish late (arrive about 0945, leave about 18:20) to avoid the traffic. If I had to be there by 0900, I'd have to allow 45 minutes to get there!
A Pedelec will allow me to achieve consistent journey times, and allow me to start and finish at more conventional times.
Reason 3 - exercise
I want to get fitter, so biking to work makes sense. Why did I buy a pedelec, rather than stick with human power?
I can get to work faster without getting hot and sweaty. It's flat or downhill all the way to work, but getting home can be a drag particularly after a hard day at the coal face!
Reason 4 - bad knees, and fun!
I enjoy riding a bike, but my knees aren't great, so having a bit of assistance will really help.