Its faster and easier to get a prototype or very simple (non-polished) app working that does not rely on specific api's to the mobile too much. So basically you will manage to get 80% done more quickly with the cross platform tool.
However the last 20% are the very tricky part. There might be some strange bugs appearing from the cross platform tool that are hard to solve or just simply wanting to achieve a very polished app with smooth transition and the latest 'native' UI components and UI paradigms (e.g. Android Lollipop).
I also had a few major bugs coming from the interface between the native SDK and the cross platform framework. One example was that suddenly the phone fonts for some Asian languages were not displayed anymore. These problems often happened when there were some SDK changes on Android or iOS and the cross platform framework had to catch up with these changes.
Compared to native developments its also way harder to find good libraries and solve bugs (e.g. via stack overflow) because there are just way less people developing with these cross platform tools.
Since last year I stopped all cross platform developments and are now developing for iOS and Android natively and I realised that I am actually developing IN SUM faster natively then before with the cross platform tools. Main reason for this is that I have a huge focus on polished and high performing UI's and in the past I wasted a huge amount of hours just to fight the weaknesses of the cross platform tools.
So my recommendation for all who want to develop polished and professional iOS and Android Apps is now to go the native route from the beginning. Its better to try and save time by shifting some code to the server side (if you have a mobile app that extends a web app) and by developing a great abstract documentation/specification that can then be quickly implemented in the respective native language.