For example, look at Libya (and North Africa in general). The Jihadi groups there used to be small and weak, and in the case of Libya the likes of Ansar al-Sharia were under the heel of Qaddafi and couldn't do much. With Qaddafi's downfall they became stronger, but were still a local problem. Now, ISIS has expanded to the region, and the Libyan Ansar al-Sharia, the Tunisian Ansar al-Sharia, and the Egyptian Ansar Bayt al-Maqdis are getting affiliated.
Move a little south of those groups and you come across Al Qaeda in the Islamic Maghreb, which has always been an issue for Mali, Algeria and Libya. AQIM probably covers the most ground of any of the Jihadi groups, but because it has largely been a local problem it has been ignored. However, AQIM has been getting closer to Boko Haram, the Nigerian bogey man that has killed over 5,000 in less than two years. Again, Boko Haram has largely been ignored because it is primarily a local issue, but the head of BH just pledged allegiance to ISIS.
Head over to the East and you find Al Shabaab, which has killed around 400 of my people in two years. They had already pledged allegiance to Al Qaeda some years back, but it appears that with the rise of ISIS they may be changing allegiance soon. Additionally, the crisis in Yemen has led to a lot of refugees moving from Yemen to Somalia (just across the sea), and there might be cross-pollination with Al Qaeda in the Arabian Peninsula (AQAP).
Going even further east, you find Abu Sayyaf in the Philippines meshing with Jemaah Islamiya in Indonesia, and both groups having affiliation with Al Qaeda (and maybe soon ISIS, considering Al Qaeda hasn't 'done much' lately).
My point? As these groups, particularly ISIS, take more ground, they will eventually do away with any opposition - be it from government or competing Jihadi outfits - and end up controlling more land, and as a result, more cashflow and more followers. Once that is done, the main target will be the US.
I understand that some may say that will be the best time to hit them, but I'd rather destroy a crocodile in its shell than when it is some 16 foot leviathan trying to introduce me to its gullet.
These groups are not a problem to the West now, but they will eventually be a huge problem. Especially considering that some of those fighting for the likes of ISIS have Western passports.
Spot on analysis and correct action direction. There’s also a benefit in not completely eliminating these local threats. They attract Western jihadis and act as a jihadi-sink. A dead jihadi is no longer a threat.