Further to Parson comments about time to command, remember in the corporate and night freight sector the hours flown per year can be quite low (ie: 200 to 300 per year), therefore low houred pilots are rarely employed because it simple takes too long for them to unfreeze the ATPL. Or this will limit the number of low houred pilots that can be employed due to the need to
keep a flow of pilots ready to take command within a few years.
The other factor is insurance policies, especially in the corporate sector, where the insurance company may specifiy minimum hours for crews.
So I will to an extent accept the comment that FI hours are not that relevant to airline flying, but the key thing is instructing does help develop spare capacity when flying, which is always useful. The other thing is instructing at the right location (ie: an airfield which has commercial operators based there) means that you don't have to make an effort to network, you will by default just meat people involved in commercial flying as a daily occurence. I will admit, flying instruction isn't a quick route to a job but it is a very enjoyable, also the more interesting jobs in the industry are certainly ones you can get with 700+ hours in the logbook.