A single degree (e.g. BA, BSc, BCom) generally works like this: you do 2 whole years of the subject, and have 1 whole year's worth of 'elective' which can be pretty much anything you want to study.
Commerce | Commerce | Electives |
Commerce | Commerce | Science | Science |
A double degree combines both, then deletes the 'elective' years, as one degree acts as the elective part of the other and vice versa^^. This ends up being 4 years. So no, you aren't doing 6 years of work in 4 years, you're just doing 4 years of study.
Engineering is a bit of a different story as there is less elective space and flexibility, but the 'combining' works in a similar fashion.
capabilities to balance time and studies. This would probably mean you have a higher chance at getting employed at top firms/ positions.
A double degree does not mean double the workload - you do the same amount of work as a single degree, just for a longer period of time. Employers are not going to think that you put in twice as much effort at uni therefore deserving the position more.
If you have 2 areas of interest (that can't be completed in 1 degree as a double major or major+minor), or you just want to broaden your horizons, then a double degree is a great idea as it affords you that breadth.
Doing a masters (as opposed to a double) will allow you to further specialise in a field (generally) rather than going broader. You shouldn't be tossing up between masters and a double degree - if you are interested in a double, don't hold that off with the intention of doing a masters instead - you can always do the masters later (even part time while you're working - your employer might even pay for it!). A disadvantage of a masters is that they usually are quite expensive.
All in all, it really depends on what
you are interested in.