A line of Syriac is a run of joined letters written right to left, with word spacing that a cursive hand can reduce to very little. There is no capitalisation, the earliest writing carries no vowel points, and several letters differ only in a dot. Reading it fluently is a matter of finding landmarks first and letters second.
Lamadh is the best landmark the script has, because it rises clear of the line. A reader scanning a page sees the ascenders before anything else, and since lamadh is also the letter of a very common prefix, those ascenders tend to fall at the beginnings of words. Nun and kaph give a second kind of landmark, descending below the line in their final forms, so a practised eye picks up word ends from below and word beginnings from above.
The rest of the segmentation comes from the eight letters that do not join to the letter after them. A break inside a line is either a word boundary or one of those eight, and both are useful.
None of this is decoration and none of it was designed. It is what a joined script accumulates when it is used for centuries by scribes who need to read fast, and it is why an unpointed manuscript that looks impenetrable to a beginner is entirely legible to someone who has learned where to look. The pointing systems came later and were added on top of a page that was already readable.