The recommended FieldTrip path settings are explained in this frequently asked question.

The code in the ft_defaults function will execute only once and preferably should be called by you in your startup.m file. The main FieldTrip functions will also call ft_defaults to ensure that the subdirectories with teh code that they rely on are added to the path.

The ft_defaults will also add some toolboxes from external to your path, such as external/signal, external/stats and external/image. These contain drop-in replacements for some MATLAB functions to reduce the requirements on the (network) licenses, which are often available in a limited number.

If you don't want these replacement functions on your path, you should do the following in your startup.m file.

[ftver, ftpath] = ft_version;
rmpath(fullfile(ftver, 'external', 'signal'))
rmpath(fullfile(ftver, 'external', 'stats'))
rmpath(fullfile(ftver, 'external', 'image'))