This is a good question because it is a very overlooked topic and the Ottomans are often brushed off as this incompetent force at the mercy of the Russians in the Caucasus and the British in Mesopotamia. Let us look at a few decisive examples as to why that wasn't always the case.

The most obvious, Gallipoli. The Allies had a few sound objectives which required Turkey to exit the war as soon as possible. Firstly, it would free up troops defending the valuable areas of the British Empire in the Middle East. Secondly, the Allies were deeply concerned about the threat of jihad in their colonies. One of the key reasons the Germans were keen on having Ottoman support was the position of the Sultan as Caliph and his (supposed) ability to call up Muslims across the world to revolt which would have seriously threatened the security of British and French (perhaps Russian too) dominions. Thirdly, it would offer relief to the Russian troops in the Caucasus and open up the only ice free route to support their armies. Finally, after the Marne the war on the Western Front had become static and a stunning victory against a component of the Central Powers was ideal.

In short, the Allies achieved none of these. Nearly half a million Allied troops were tied down in the Dardanelles suffering many casualties shocked by the tenacious spirit and resistance the Ottomans put up. Many letters home speak of the courage and resilience of "Abdul". The defense made by the Turks freed them of the humiliation of the earlier Balkan Wars and allowed commanders to test their mettle and continue to spar successfully with the British in future campaigns.

The Siege of Kut: After Gallipoli, the Allies were on the defensive. Despite a fantastic effort by the Indian Army to carve its way through Mesopotamia unbeaten, things were not looking so rosy. Ottoman forces were pressing into Yemen and threatening the port of Aden and Libyans under the command of Turkish officers had seceded land in Egypt. There was a belief for every victory the Ottomans made, German propaganda would incite jihadist revolt in the Allied colonists and that needed to be stopped. Now, overextended British forces had allowed themselves to be surrounded in the town of Kut (roughly between Basra and Baghdad) with over 7000 troops trapped. Breaking out was put to bed by determined Ottoman forces and relief was denied. At one point, Lord Kitchener even proposed trying to bribe the Ottomans to let the soldiers out of Kut. The eventual surrender was a huge blow to the British making their plan of knocking out the "weak link" of the Central Powers a humiliation. For the Turks, it was another victory that fuelled their confidence.

Throughout both these debacles, the Allies were increasingly fearful of the threat of impending jihad. With hindsight, this never came to light but remained a deeply concerning threat if the Ottomans continued to claim success. Much of these victories were defensive and a reaction to Allied initiatives to try and end their participation in the war as opposed to the Turks proactively trying to conquer Allied possessions. Some argue that the Allies should have maintained an entirely defensive posture as the Turks simply were not worth the manpower and had no bearing on victory in the Western Front. However, the threat of jihad was deeply troublesome for the colonial powers and in their mind warranted active assault on the Ottoman Empire. Perhaps their greatest impact is the fact that after Kut the British turned to another religious power in the region, the Sharif of Mecca ultimately resulting in the Arab Revolt and the troublesome post-war debate over Arab Nationalism and the fate of the newly independent countries.

Sources:

Rogan E, The Fall of the Ottomans (London 2015)

Stevenson D, 1914-1918 The History of the First World War (London 2004)